1. Field of the Invention
This invention relates to a chemical vapor deposition system for depositing coatings on glass sheet substrates.
2. Background Art
Coatings have previously been applied to glass sheet substrates to make semiconductor devices such as photovoltaic panels. One way in which such coatings are applied is by chemical vapor deposition. Close-spaced sublimation was previously utilized to apply coatings such as cadmium sulfide and cadmium telluride to a glass sheet substrate by inserting the substrate on a batch basis into a sealed chamber that is then heated. The glass sheet substrate in close-spaced sublimation is supported at its periphery in a very close relationship, normally two to three millimeters, to a source of material of cadmium telluride. The heating by such a process proceeds to about 450xc2x0 to 500xc2x0 C. whereupon the cadmium telluride begins to sublime very slowly into elemental components and, upon reaching an temperature of about 650xc2x0 to 725xc2x0 C., the sublimation is at a greater rate and the elemental components recombine at a significant rate on the downwardly facing surface of the substrate.
Continuous processing of thin films onto glass sheet substrates is disclosed by U.S. Pat. No.: 5,248,349 Foote et al., U.S. Pat. No. 5,372,646 Foote et al., U.S. Pat. No. 5,470,397 Foote et al., and U.S. Pat. No. 5,536,333 Foote et al. The chemical vapor deposition utilized to provide the continuous coating is performed within an oven that defines a heated chamber and that is located within an enclosure. A roll conveyor has rolls that extend through the oven to support a glass sheet substrate on which the coating is performed and a drive mechanism located internally of the enclosure but externally of the oven drives the ends of the conveyor rolls which project outwardly from the oven. Also, U.S. Pat. No. 5,945,163 Powell et al. and U.S. Pat. No. 6,037,241 Powell et al. disclose apparatus for performing chemical vapor deposition wherein the gaseous material to be deposited is passed through a heated permeable membrane from a material supply for deposition on the substrate.
An object of the present invention is to provide an improved chemical vapor deposition system for providing coatings on glass sheet substrates.
In carrying out the above object, the chemical vapor deposition system of the invention includes a housing that defines an enclosed deposition chamber and includes a lower portion and an upper portion having a horizontal junction with each other. A seal assembly extends between the lower and upper housing portions at their horizontal junction to seal the deposition chamber. A roll conveyor located within the deposition chamber conveys glass sheet substrates along a direction of conveyance at a plane of conveyance below the horizontal junction of the lower and upper housing portions where the seal assembly is located. A chemical vapor distributor is located within the deposition chamber above the roll conveyor to provide chemical vapor deposition of a coating on the conveyed glass sheet substrates. The housing includes an entry through which the glass sheet substrates to be coated are introduced into the deposition chamber at a location below the horizontal junction of the lower and upper housing portion where the seal assembly is located, and the housing also includes an exit through which the coated glass sheet substrates leave the deposition chamber at a location below the horizontal junction of the lower and upper housing portions where the seal assembly is located.
The deposition system includes a vacuum source for drawing a vacuum within the deposition chamber. The seal assembly between the lower and upper housing portions includes inner and outer seal members spaced from each other to define an intermediate seal space that is located between the deposition chamber and the ambient and in which a vacuum is drawn to a lesser extent than in the deposition chamber. A sensor detects the pressure within the seal space to sense leakage of either the inner seal member or the outer seal member. The seal assembly includes lower and upper seal flanges on the lower and upper housing portions, and the inner and outer seal members extend between the lower and upper seal flanges to seal between the lower and upper housing portions. Clamps extend between the lower and upper seal flanges to secure the upper housing portion to the lower housing portion. Each clamp includes a hydraulic cylinder operable to provide the securement between the lower and upper seal flanges.
The deposition system includes an oven located within the housing and having elongated heaters that extend along the direction of conveyance in laterally spaced banks to heat the conveyed glass sheet substrates and control temperature differentials of the substrates laterally with respect to the direction of conveyance. Each elongated heater includes an electric resistance element through which electricity is passed to provide heating, and each heater includes an elongated quartz tube through which the electric resistance element extends. The roll conveyor includes rolls that extend through the oven and have ends projecting outwardly therefrom within the housing, and a drive mechanism engages and rotatively drives the roll ends outwardly of the oven within the housing.
The deposition system also includes a screen that is located below the roll conveyor to catch any broken glass sheet substrates. The screen is made of stainless steel and includes stiffeners.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the preferred embodiment when taken in connection with the accompanying drawings.